Diffcoeff version 5 tilde

Question

my distribution updated diffcoeff to version 5.3 and now a lot of stuff is broken:

1. Powers of \dl, e.g. \dl^2 x don't work anymore (See Powers of \dl with diffcoeff)
2. Symbols with a tilde on them don't work anymore:

\documentclass[11pt,parskip]{scrartcl}
    
\usepackage{lmodern}
\usepackage[ngerman]{babel} 
\usepackage[utf8]{inputenc}
\usepackage[T1]{fontenc}  \usepackage{amsmath}
    
% use option ISO or version >=5 (not tested) to get upright d
\usepackage{diffcoeff}
    
\begin{document}
  $\dl A$
  $\dl \tilde{A}$
  %$\dl^2 A$    
\end{document}

does not compile with the error

! You can't use math shift character $ after \the.
<argument> $
            
l.14 $\dl \tilde{
                 A}$

The obvious fix for both problems is using \usepackage[ISO]{diffcoeff}[=v4] but in my opinion that's not a long term solution. Considering the first problem, a fix is available, does anyone know how to fix the second problem?

Also, I switched from the physics package because the overall opinion seems to be that it is badly programmed, but when old documents break with newer version of the diffcoeff package I might switch back. Is there any advice for avoiding such problems in the future?

Thanks in advance.

Answer 1

As of version 5, you need to put a multi-token variable in braces after \dl, such as $\dl{\tilde{A}}$.

This is explained in section 4.1 "Differentials" (on page 48) of the current manual (version 5.3).

MWE:

\documentclass{article}
\usepackage{diffcoeff}
    
\begin{document}
  $\dl A$
  $\dl{\tilde{A}}$
  $\difc[2]A{}$    
  $\difc[2]{\tilde{A}}{}$    
\end{document}

---

Your second question about "hardening" documents against future package changes cannot be answered easily. In general, package maintainers are advised to take care for backwards compatibility, so that such problems don't occur at all. But at some point in time, best practices may change, new packages offering better basic functionality may emerge and new standards may be established, which would eventually make it necessary to alter the syntax of certain commands in a package. At least, such big changes should typically be documented in the package manuals (and this is the case here).

There is no sensible way to protect against this, apart from freezing a project including all the packages in the current working version for future reference. A better advice might be to always use up-to-date packages and also update your documents from time to time (but I know that this can be tedious).